As an image forming apparatus of an electrophotographic system, such as a laser printer, a digital copying machine, or a laser facsimile, there is a type in which a toner image formed on a photoconductor is primarily transferred to a transfer belt, and the toner image primarily transferred on the transfer belt is further secondarily transferred to a recording sheet. In this type of image forming apparatus, a transfer apparatus includes a primary transfer unit having a transfer belt and a secondary transfer unit having a secondary transfer roller.
The primary transfer unit includes, for example, a drive roller, a secondary transfer opposite roller, and a primary transfer roller, and the transfer belt is stretched over the drive roller and the secondary transfer opposite roller and is rotated. The primary transfer roller is disposed at a position inside of the transfer belt and opposite to the photoconductor, and a specified potential is applied to the primary transfer roller so that the toner image on the photoconductor is primarily transferred to the outer periphery of the transfer belt.
The secondary transfer roller of the secondary transfer unit and the secondary transfer opposite roller of the primary transfer unit form a nip through the transfer belt. A recording sheet contained in a paper feeding section passes through a specified conveyance path and passes through the nip. When the recording sheet passes through the nip, a specified potential is applied to the secondary transfer roller, and the toner image primarily transferred on the outer periphery of the transfer belt is secondarily transferred to the recording sheet.
The secondarily transferred toner image is fixed by a fixing apparatus, and then is discharged to a discharge tray or the like included in the image forming apparatus.
When the recording sheet passes through the conveyance path or passes through the nip, paper jamming may occur due to some cause.
In order to enable a user to remove the jammed recording sheet, the secondary transfer unit is constructed to be openable and closable relative to the outside of the main body of the image forming apparatus. For example, the lower side of the secondary transfer unit is supported to be rotatable around a support shaft provided at the main body of the image forming apparatus, and a hook to be hooked on a fixing member provided at the main body of the image forming apparatus is provided on the upper side of the secondary transfer unit. In a standing state in which the secondary transfer unit is closed, the hook urged by a spring or the like is hooked on the fixing member, and the secondary transfer unit is fixed to the main body of the image forming apparatus. When the secondary transfer unit is opened, the user operates a handle lever or the like provided at the outside of the secondary transfer unit to release the hooking between the hook and the fixing member, and opens the secondary transfer unit to the outside of the apparatus while rotating it around the support shaft.
In addition to this, there is a type in which a magnet is provided on the upper side of the secondary transfer unit, and the secondary transfer unit is fixed to the main body of the image forming apparatus by the magnetic force of the magnet.
As stated above, in the transfer apparatus (or the image forming apparatus) of the related art, the dedicated opening and closing mechanisms (the foregoing hook, spring, handle lever, magnet, etc.) for opening and closing the secondary transfer unit are required, and these opening and closing mechanisms cause the increase of the number of parts of the whole apparatus and cause the increase of cost.